Electromigration failure distribution of contacts and vias as a function of stress conditions in submicron IC metallizations

Electromigration testing of integrated circuit metallizations requires the use of accelerated testing. Accurate extrapolation to circuit operating conditions requires a thorough understanding of the impact of the accelerated stress conditions on the parameters of the failure distribution. In this paper we examine the dependence of the dispersion of the failure time (/spl sigma/) on current density and resistance failure criterion for contacts to silicon. We show that a depends on current density, and rapidly increases as it approaches the current density threshold for electromigration, while /spl sigma/ unaffected by the resistance failure criterion for a bond pad terminated test structure. We model the failure time dispersion as arising from variability in conductor geometry. The model shows that the current density dependence of /spl sigma/ is an inherent property of electromigration at contacts/vias, and that it arises from variability in the current density between samples. The model provides a means of quantifying contributions to a from the manufacturing process and accelerated testing conditions.